A known method for determining pore space properties and matrix thermal conductivity in a porous material sample consists in measuring thermal conductivity of the sample alternately saturated by three fluids with different thermal conductivity (Popov et al. Interrelations between Thermal Conductivity and Other Physical Properties of Rocks: Experimental Data, Pure and Applied Geophysics., 160, 2003, pp. 1137-1161). The method is based on determination of porosity of the porous material sample and shapes of pores and cracks simulated by spheroids and characterized by a single aspect ratio. Porosity of the porous sample, thermal conductivity of its matrix, and the aspect ratio of pore and crack simulating spheroids are determined through solving three non-linear equations with three unknowns, using thermal conductivity values as measured in the porous sample alternately saturated by the three fluids with known different thermal conductivity. Equations in that system are equalities of theoretical and experimental thermal conductivity values of porous samples successively saturated by three fluids with known and different thermal conductivity. Theoretical values of thermal conductivity are determined by a known method based on a self-consistent effective-medium theory which allows for thermal conductivity of a porous material to be expressed as a function of thermal conductivity of its matrix, the fluid saturating its pores and cracks, porosity and the aspect ratio of spheroids. The disadvantages of the method are as follows: (1) a single aspect ratio is used to characterize pore shapes and cracks, even though their actual aspect ratios differ by several orders of magnitude, (2) the method requires successive saturation of a porous material sample with three fluids with thermal conductivity meeting the three following criteria: a) it should be known for each fluid used; b) it should have materially different values, each of which should be pre-selected in conformity with certain requirements regarding thermal conductivity, porosity and pore space parameters of heterogeneous porous materials under study; c) thermal conductivity values of the three fluids in question should be within a certain range pre-selected depending on thermal conductivity, porosity and pore space parameters of heterogeneous porous materials under study. Meeting the last three criteria is a serious challenge because of a shortage of such fluids in the natural environment. Furthermore, that well-known method has the disadvantage of insufficient accuracy of definition of pore space parameters and matrix thermal conductivity because it is limited to measurements of merely thermal conductivity of fluid-saturated heterogeneous porous material, and fails to use measured values of other physical properties, which may include, for instance, velocities of longitudinal and shear elastic waves, electric conductivity, hydraulic and dielectric permeability, density, and volumetric thermal capacity.
There is also known a method for characterizing pore space and thermal conductivity of a matrix (Popov et al. Physical Properties of Rocks from the Upper Part of the Yaxcopoil-1 Drill Hole, Chicxulub Crater, Meteoritics & Planetary Science, 39, #6, 2004, pp. 799-812) which comprises successive saturation of a porous sample with at least two fluids with known different thermal conductivities to determine porosity of the sample. Each time after the porous sample is saturated by a fluid its thermal conductivity is measured, and a combination of measured thermal conductivity and porosity values of the porous sample of a known ratio are used to determine pore space and thermal conductivity of the porous sample matrix.
That known method has the following disadvantages: (1) more than two unknowns are determined from merely two thermal conductivity measurements, which may result in a fairly wide range of solutions in determining pore space parameters and matrix thermal conductivity; (2) porosity should be preliminary known; (3) the method requires successive saturation of a porous material sample with two different fluids with thermal conductivity meeting the following criteria: a) it should be known for each fluid; b) it should be materially different within a pre-selected range in conformity with thermal conductivity, porosity, and pore space parameters of heterogeneous porous materials under study. Meeting the last two criteria is a serious challenge because of a shortage of such fluids in the natural environment. Furthermore, a disadvantage of that well-known technique is insufficient accuracy of definition of pore space parameters and matrix thermal conductivity because it is limited to measurements of merely thermal conductivity of fluid-saturated heterogeneous porous material, and fails to use measured values of other physical properties, which may include, for instance, velocities of longitudinal and shear elastic waves, electric conductivity, hydraulic and dielectric permeability, density, and volumetric thermal capacity.